Detecting defects within printed material has generally been a manual process. In such a case, a person manually views a printed item to see if any defects are apparent. This can be a time consuming and expensive process.
Some methods exist for using scanning technology to detect print defects. However, these methods use precise spatial and intensity alignments and are sensitive to even small noise perturbations. This results in a high rate of false defect detections and detection of acceptable defects that would not be considered defects. Further, some such detected defects may not even be perceivable by a person.
Other methods exist to detect texture defects in prints or on surfaces. However, these methods do not work well with printed items containing various types of content, including pure line art works, natural images, text, and combined documents.